1. Field of the Invention
This invention relates to the field of expandable tubulars and more specifically to the field of expanding tubulars with multiple expansion swages.
2. Background of the Invention
Expandable tubulars have become a viable technology for well drilling, repair, and completion. In a conventional technique for expansion, an expansion swage is positioned inside a pre-expanded portion of a tubular that is sealed at the bottom with a plug. Hydraulic pressure is applied through the drill pipe into the pre-expanded portion of the tubular generating sufficient force to propagate the expansion swage and radially expand the unexpanded portion of the tubular. Drawbacks to such conventional technique include that the expansion pressure may be limited by the yield pressure of the expanded portion of the tubular, which may limit the degree of expansion. Further drawbacks include the ratio of the expandable tubular diameter to its wall thickness, which may be due to the maximum pressure available on drilling rigs. Consequently, conventional techniques may typically be limited to expansion ratios of 10-16% and to a collapse resistance of 3,000-4,000 psi.
Other conventional techniques for expansion include using a hydraulic actuator to generate force for propagating an expansion swage and radially expanding a tubular. The force is applied against a front anchor or a back anchor, which results in compressive or tensile stresses in the tubular. The connectors in the expandable tubulars, due to geometrical constraints, are typically of flush or a near flush type, which typically results in a tensile efficiency of 50%. Drawbacks include that the expansion force may not be higher than 50% of the tubular body yield strength, which may limit the degree of tubular expansion to 25-28%.
Another technique includes lowering the friction coefficient (i.e., by lubricants) between the tubular and the expansion swage, which may reduce the value of the friction factor. Drawbacks include the cost and efficiency of such a technique.
Consequently, there is a need for a technique that provides expandable tubulars with significantly higher performance characteristics, including collapse resistance, and higher expansion ratios.